Particle detection via resonant frequencies

Abstract

In one example in accordance with the present disclosure, a particle detection system is described. The particle detection system includes a microfluidic channel through which fluid is to flow. The fluid includes particles. The particle detection system also includes a sensing circuit to output a resonant frequency. The sensing circuit includes a pair of electrodes disposed within the microfluidic channel. Contents of a volume between the pair of electrodes changes a capacitance between the pair of electrodes. A change in the capacitance changes the resonant frequency output by the sensing circuit. The particle detection system also includes a controller to determine the contents of the volume based on the resonant frequency.

1 . A particle detection system, comprising:
 a microfluidic channel through which fluid is to flow, wherein the fluid comprises particles;   a sensing circuit to output a resonant frequency, wherein:
 the sensing circuit comprises a pair of electrodes disposed within the microfluidic channel; 
 contents of a volume between the pair of electrodes changes a capacitance between the pair of electrodes; and 
 a change in the capacitance between the pair of electrodes changes the resonant frequency output by the sensing circuit; and 
   a controller to determine the contents of the volume based on the resonant frequency.   
     
     
         2 . The particle detection system of  claim 1 , further comprising a database to map resonant frequency to contents of the volume. 
     
     
         3 . The particle detection system of  claim 2 , wherein:
 the controller is to convert the resonant frequency output by the sensing circuit to a capacitance; and   the database is to map the capacitance to contents of the volume.   
     
     
         4 . The particle detection system of  claim 1 , further comprising a comparator to convert the resonant frequency output by the sensing circuit to a step function. 
     
     
         5 . The particle detection system of  claim 1 , wherein the pair of electrodes are disposed inside of a constriction along the microfluidic channel. 
     
     
         6 . The particle detection system of  claim 1 , wherein the pair of electrodes are disposed outside of a constriction along the microfluidic channel. 
     
     
         7 . The particle detection system of  claim 1 , wherein the fluid is drawn through the microfluidic channel via an inkjet ejector. 
     
     
         8 . The particle detection system of  claim 1 , wherein the sensing circuit further comprises:
 an inductor outside the microfluidic channel; and   a switch to introduce multiple frequencies into the sensing circuit.   
     
     
         9 . A method, comprising:
 introducing multiple frequencies into a sensing circuit, wherein:
 a pair of electrodes are disposed within the microfluidic channel; and 
 a fluid with particles disposed therein flows between the pair of electrodes; 
   identifying a resonant frequency of the sensing circuit, the resonant frequency defined in part by the capacitance of a volume between the pair of electrodes; and   determining the contents of the volume based on an identified resonant frequency.   
     
     
         10 . The method of  claim 9 , wherein introducing multiple frequencies comprises closing a switch to couple a voltage source to the sensing circuit. 
     
     
         11 . The method of  claim 9 , further comprising:
 converting the resonant frequency into a step function; and   counting a number of steps.   
     
     
         12 . The method of  claim 9 , wherein determining the contents of the volume comprises determining a quantity of particles within the volume. 
     
     
         13 . The method of  claim 9 , wherein determining the contents of the volume comprises determining a type of particle within the volume. 
     
     
         14 . A particle detection system, comprising:
 a microfluidic channel through which fluid is to flow, wherein the fluid comprises particles;   a sensing circuit to output a resonant frequency, the sensing circuit comprising:
 a pair of electrodes disposed within the microfluidic channel; 
 a voltage source to apply a voltage through the sensing circuit; 
 a switch to drive multiple frequencies of the voltage into the sensing circuit; 
 an inductor; and 
 a frequency counter to determine the resonant frequency of the sensing circuit, 
   wherein:
 contents of a volume between the pair of electrodes changes a capacitance between the pair of electrodes; and 
 a change in the capacitance changes the resonant frequency output by the sensing circuit; and 
   a controller to determine the contents of the volume based on the resonant frequency.   
     
     
         15 . The particle detection system of  claim 14 , wherein the controller, responsive to an output of the sensing circuit, is to control a fluid ejection system in which the particle detection system is disposed.